With an increase in capacity of information processing in recent years, various information recording technologies have been developed. In particular, the surface recording density of an HDD using a magnetic recording technology is continuously increasing at an annual rate of approximately 100%. In recent years, an information recording capacity exceeding 200 gigabytes per perpendicular magnetic recording medium with a 2.5-inch diameter for use in an HOD or the like has been demanded. To fulfill such a demand, an information recording density exceeding 400 gigabits per square inch is desired to be achieved.
To achieve a high recording density in a magnetic recording medium for use in an HDD or the like, a perpendicular magnetic recording type has been proposed in recent years. In a perpendicular magnetic recording medium for use in the perpendicular magnetic recording type, the axis of easy magnetization of a magnetic recording layer is adjusted so as to be oriented in a direction perpendicular to the base surface. In the perpendicular magnetic recording type, compared with a conventional in-plane recording type, it is possible to more suppress a so-called thermal fluctuation phenomenon, in which thermal stability of a recording signal is impaired because of a superparamagnetic phenomenon to cause the recording signal to be lost, and therefore the perpendicular magnetic recording type is suitable for increasing the recording density.
As a magnetic recording medium for use in the perpendicular magnetic recording type, a CoCrPt—SiO2 perpendicular magnetic recording medium (refer to Non-Patent Document 1) has been proposed because of high thermal stability and excellent recording characteristic. This is to configure a granular structure in a magnetic recording layer in which a non-magnetic grain boundary part with segregation of SiO2 is formed between magnetic particles in which a crystal with an hcp structure (a hexagonal close-packed crystal lattice) of Co continuously grows in a columnar shape, thereby achieving finer magnetic particles and an improvement of a coercive force Hc together. It is known that an oxide is used for the non-magnetic grain boundary (a non-magnetic portion between magnetic particles), and, for example, using any one of SiO2, Cr2O3, TiO, TiO2, and Ta2O5 has been proposed (Patent Document 1).
However, when an intense magnetic field is applied to the magnetic recording layer, leak field to an adjacent track becomes large, so that WATE (wide Area Track Erasure), namely, a phenomenon, that recorded information within the range of several micrometers from a track to write on is lost, is problematic. As means for reducing WATE, it is important to set a reversed magnetic domain nucleation field Hn of the magnetic recording layer at a negative value, and increase the absolute value thereof. In order to obtain a high (large in absolute value) Hn, a CGC (Coupled Granular Continuous) medium in which a thin film having a high perpendicular magnetic anisotropy is formed above or below the magnetic recording layer having a granular structure was devised (Patent Document 2).
Generally, as the coercive force Hc of the magnetic recording layer is more improved, a higher recording density can be achieved but writing by the magnetic head tends to be more difficult. Then, an auxiliary recording layer improves saturated magnetization Ms and also contributes to improving easy writing, namely, an overwrite characteristic. In other words, objects of disposing the auxiliary recording layer on the magnetic recording layer are to improve the reversed magnetic domain nucleation filed Hn to reduce noise, and to improve the saturated magnetization Ms to improve the overwrite characteristic. Note that the auxiliary recording layer may be referred to as a continuous layer or cap layer.
With such increase in information recording density, both a line recording density in a circumferential direction (BPI: Bit Per Inch) and a track recording density in a radial direction (TPI: Track Per Inch) keep increasing. Furthermore, a technique of reducing a space (magnetic spacing) between the magnetic layer of the magnetic disk and a recording and reproducing device of the magnetic head to improve an S/N ratio is also considered. The flying height of the magnetic head that has been desired in recent years is 10 nm or less.
As a technique for reducing magnetic spacing such as described above, there has been proposed a DFH (Dynamic Flying Height) head that causes a magnetic head element to generate heat during operation of the magnetic head element and causes the heat to thermally expand the magnetic head, thereby projecting the magnetic head slightly in the direction of an ABS (The air bearing surface). This makes it possible to adjust the space between the magnetic head and the magnetic disk so that the magnetic head can fly with the magnetic spacing kept stable and narrow.
The perpendicular magnetic recording disk is provided with a protective layer that protects the surface of the magnetic recording layer from being damaged when the magnetic head hits the perpendicular magnetic recording disk. The protective layer forms a coating film with a high hardness by a carbon overcoat (COD), namely, a carbon coating film. The protective layer may be a layer made of hard diamond-like (amorphous) carbon and soft graphite carbon in a mixing manner (for example, Patent Document 3). A technique of manufacturing a diamond-like carbon protective layer by CVD (Chemical Vapor Deposition) method has also been disclosed (for example, Patent Document 4).
On the protective layer, a lubricating layer is also formed to protect the protective layer and the magnetic head when the magnetic head hits the disk. The lubricating layer is formed, for example, by applying perfluoro polyether and sintering the same.